Louse Fly

2015 December 12

Rosie spotted this freaky-looking fly on our windowsill on October 3, 2015. It has unusually strong legs, peculiar “toes”, and an oddly-shaped head with its proboscis pointing straight forward.

The body is kind of flattened, as if it is adapted for squeezing into tight spaces.

It looked kind of like something that I’d heard about before, called sheep keds, which are wingless flies that have become external parasites similar to ticks. Of course, this one obviously isn’t that exactly because it has wings, but the head sure looks like something a bloodsucker would have.

And when I followed up by checking on the family that sheep keds are in (the Louse Flies, family Hippoboscidae), this certainly looked like the right group, right down to the leg structure, the head shape, and the odd “muscled” pattern on the back of the thorax.

Specifically, the bird-parasitizing louse flies in the genus Icosta look pretty close. This is a genus of about 50 louse flies that each specialize in their own kind of bird. That body shape makes it possible for them to work their way in between a bird’s feathers so that they can get to the skin, and the front-facing proboscis lets them drive right in for the blood. And I expect that those peculiar toes on their feet are probably specifically for gripping feathers.

I don’t know for sure which kind of bird this one came off of, although I expect it is from the ones that come around the feeders behind our house. Most likely one of the larger birds, since this is a pretty big parasite to go after little things like hummingbirds and sparrows. Right about the time that Rosie found this fly, the bluejays were seriously going to town on the 8-foot-tall sunflowers that Sam had grown right there by the back door, so if I had to guess I’d say that it most likely came off of one of the jays.[1]

The females evidently only have one egg at a time, which hatches internally where she feeds it a “milk” secretion in her uterus until it is almost ready to pupate. The larva is then “born alive” either on the host bird, or in the soil at a location where it will be able to pupate, and then find a new host as soon as it becomes an adult. The female lives as an adult for several months, and can have around 20 or so offspring.

[1] Although, come to think of it, I think this might have been the day after the ruffed grouse slammed into our dining room window and killed itself[2]. Something must have startled it from the top of the hill south of our house, and it thought that our dining room looked like a nice, cave-like refuge. If anything was going to knock the parasites off of a large bird, that would have done it. Honestly, I’m surprised it didn’t break the window. It sounded like a bomb going off.

[2] And yes, it was pretty delicious. Sandy knows exactly how to clean and cook grouse. And this time, there was no need to pick out shotgun pellets.

One Response
  1. Carole permalink
    December 12, 2015

    Interesting, will be on the look out for this type of fly

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